1. Field of the Invention
The present invention relates to push rod tubes for automobile engines and more particularly to a push rod tube for a flat four opposed cylinder air cooled Volkswagen engine which utilizes high lift rocker arms for increased volumetric efficiency of the engine.
A problem which occurs in the operation of Volkswagen engines after high lift rocker arms have been installed is that the push rod operating parameters are displaced from the designed operating path and the push rods reciprocate at a location closer to the walls of the push rod tubes than was intended by the original design of the engine. The lateral displacement of the push rods is sufficient that under certain conditions and excursions there can be mechanical interference between the push rods and the side wall of the standard push rod tube.
In order to be able to utilize the high lift rocker arms required for increased engine breathing and volumetric efficiency, it is necessary to provide an adequate clearance between the push rods and the interior wall of the push rod tube at the outer ends thereof in the area proximate the rocker arms where there is a possibility of interference.
2. Description of the Prior Art
A standard push rod tube for a flat four opposed cylinder air cooled Volkswagen engine is illustrated in FIG. 1 of the drawings of this specification. It discloses a push rod tube having a pair of bellows disposed integral to and disposed at opposed ends of the push rod tube and spaced from the ends thereof. In the initial design configuration, the push rod tubes are manufactured slightly longer in length than the length they are designed to assume when they are disposed in operative position between the crankcase and the cylinder heads of the engine.
The push rod tubes are shortened during the installation process by the seating of the cylinder heads onto the engine block. The space loss occurs during the cylinder head tightening operation and the length decrease is accommodated by each of the push rod tube bellows collapsing slightly. This ensures that the gaskets and seals on the ends of the push rod tubes are properly seated and compressed in their respective receptacles to seal out any dirt from penetrating into the engine and to prevent the escape of any internal engine gases and fluids during operation. The push rod tubes are not otherwise held in position by bolts or flanges but are simply held in place in captured relation between the cylinder heads and crankcase by their respective receptacles and seals.
Initial attempts to increase the diameter of the push rod tubes for the purpose of accommodating the resulting push rod lateral movement within the tubes, caused by the installation of high lift rocker arms, has been relatively unsuccessful for several reasons. One of the reasons is that a larger outside diameter bellows would interfere with the cooling fins of the cylinder head. Another reason is that a tube of standard design with a larger outside diameter at the end would not fit into the receptacle provided in the cylinder head.
Thus, it is necessary to provide another solution to the problem of interference between the push rod movement and the internal wall of the push rod tube when high lift rocker arms are utilized in a Volkswagen flat four opposed cylinder air cooled engine other than just increasing the internal diameter of the tube.